The Chicago-based independent Mac developer conference is set for its fourth …

The annual C4 developer conference, organized by Chicago-based developer Jonathan "Wolf" Rentzsch, opened up registration for this year's event early this morning, but sold out in just a few hours. The conference will take place in downtown Chicago on September 25-27, and feature a number of how-tos and presentations from all across the developer spectrum—even (gasp!) a Windows developer.

This year's conference will have the usual in-depth sessions such as a look under the hood at version control systems, the joys of unit testing, and how to delegate tasks to a team. Some of the more unusual topics on the schedule include talks on MacRuby, a Ruby implementation powered by LLVM; Cocotron, a Windows port of Objective-C and Cocoa frameworks; and the hard art of creating simple software by none other than FeedDemon developer Nick Bradbury.

In addition to the in-depth sessions, this year's schedule also includes 16 "Blitz talks"—short, five minute presentations with a maximum of 20 slides. These quick takes cover a wide array of topics, including "Building (Unsupported) Plugins for 64 Bit Applications," "Design Validation on the iPhone," "Finding the Time: Stories from a One-Man Band," and "No Pain, No Gain: Indie Nuggets from Ecamm." Appropriately, the slides will be displayed along with a countdown timer using a custom app Rentzsch wrote called Blitz.

Developers come from all over the country and world to attend C4, which is characterized by camaraderie and collaboration as much as it is by technical discussions. In indie Mac developer circles, it has become as important, if not more so, than Apple's own WWDC. If you want a chance to get in on the action this year, though, your best bet is to sign up for the waiting list. Or perhaps you can start planning to register for C4[4] next year.

UPDATE: We got in touch with Rentzsch, who let us know that despite the increased demand, there aren't any plans to expand C4. "Once you get passed a certain size, logistics and cost become almost impossible," he told Ars. In the past, he has made videos of the conference presentations available for free online, and he plans to continue that trend for those that can't make it. He also said he may experiment with a different registration process in the future to encourage more first-time attendees. Still, he encourages those who wish to attend to sign up for the waiting list. "There are always a few cancellations" every year, he said.